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Selected AbstractsRapid crystal growth without inherent supersaturation induced by nanoscale fluid flows?CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2006M. J. Jones Abstract Crystal growth is a process that only takes place under non-equilibrium conditions and a necessary prerequisite is that the crystal is exposed to a phase that is supersaturated in the material the crystal is composed of, be it a solution, a vapour or a supercooled melt. In industrial mass crystallization the growth rate for a population of crystals (in suspension growth processes [1]) rarely exceeds mean linear velocities of 10 -7 ms -1. Here we present a mass crystallization process which is accompanied by rapid crystal growth several orders of magnitude faster and into a region of solution that is without inherent supersaturation. The material investigated is a solid hydrate that exhibits a solution mediated phase transition to its anhydrous form in the presence of methanol [2]. The phase transition is initiated simply by placing an amount of hydrate crystals into the solvent and is characterized by the rapid emergence of needle-shaped crystals. The needles emanate from the crystal faces of the hydrate crystals and grow into the solution, which is nominally free of the substance to be crystallized. The high growth rate of the crystals, which of the order of up to 10 -4 ms -1 is surprising. Although rapid needle growth has been observed before [3-9], to date a satisfactory explanation for needles growing under the abovementioned conditions is still outstanding. Based upon the topology of the crystals we propose a tentative mechanism for this phenomenon capable of explaining the unusually rapid growth and highlight those questions that need addressing in order to verify this mechanism. X-ray powder diffraction is used to characterize the crystal phase of the needles; confocal fluorescence microscopy reveals that the needles are hollow. The width of these needles is between 0.5 and 5 ,m, their length appears to be limited only by the amount of hydrate available for their formation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Molecular modeling of metal complexation by a fluoroquinolone antibioticENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2008Ludmilla Aristilde Abstract An understanding of the factors controlling the chemodynamics of fluoroquinolone antibiotics in different environmental matrices is a necessary prerequisite to the assessment of their potential impact on nontarget organisms in soils and receiving waters. Of particular interest are the complexes formed between fluoroquinolones and metal cations, which are believed to be important in the mechanism of sequestration of the antibiotic by minerals and natural organic matter. The structures of these complexes have not been fully resolved by conventional spectroscopy; therefore, molecular simulations may provide useful complementary insights. We present results from apparently the first molecular dynamics simulations of a widely used fluoroquinolone antibiotic, ciprofloxacin (Cipro), in aqueous complexes with five metal cations typically found in soils and surface waters: Ca2+, Mg2+, Fe2+, Na+, and K+. The interatomic potential functions employed in the simulations were validated by comparison with available structural data for solid-phase Cipro-hexahydrate and for the metal cations in aqueous solution. Although no comprehensive structural data on the aqueous complexes appear to be available, properties of the metal complexes predicted by our simulations agree with available data for solid-phase metal,Cipro complexes. Our results indicate that the ionic potential of the metal cation controls the stability of the complex formed and that the hydration number of the metal cation in aqueous solution determines its coordination number with O atoms in the metal,Cipro complex. In respect to environmental chemodynamics, our results imply that Cipro will form two configurations of bidendate chelates with metal centers on exposed surfaces of mineral oxides, water-bridged surface complexes with exchangeable cations in clay mineral interlayers, and cation-bridged complexes with functional groups in natural organic matter. [source] Full-length prion protein aggregates to amyloid fibrils and spherical particles by distinct pathwaysFEBS JOURNAL, Issue 9 2008Driss El Moustaine As limited structural information is available on prion protein (PrP) misfolding and aggregation, a causative link between the specific (supra)molecular structure of PrP and transmissible spongiform encephalopathies remains to be elucidated. In this study, high pressure was utilized, as an approach to perturb protein structure, to characterize different morphological and structural PrP aggregates. It was shown that full-length recombinant PrP undergoes ,-sheet aggregation on high-pressure-induced destabilization. By tuning the physicochemical conditions, the assembly process evolves through two distinct pathways leading to the irreversible formation of spherical particles or amyloid fibrils, respectively. When the PrP aggregation propensity is enhanced, high pressure induces the formation of a partially unfolded aggregated protein, AggHP, which relaxes at ambient pressure to form amorphous aggregates. The latter largely retain the native secondary structure. On prolonged incubation at high pressure, followed by depressurization, AggHP transforms to a monodisperse population of spherical particles of about 20 nm in diameter, characterized by an essentially ,-sheet secondary structure. When the PrP aggregation propensity is decreased, an oligomeric reaction intermediate, IHP, is formed under high pressure. After pressure release, IHP relaxes to the original native structure. However, on prolonged incubation at high pressure and subsequent depressurization, it transforms to amyloid fibrils. Structural evaluation, using optical spectroscopic methods, demonstrates that the conformation adopted by the subfibrillar oligomeric intermediate, IHP, constitutes a necessary prerequisite for the formation of amyloids. The use of high-pressure perturbation thus provides an insight into the molecular mechanism of the first stages of PrP misfolding into amyloids. [source] Exploiting human anatomical variability as a link between genome and cognomeGENES, BRAIN AND BEHAVIOR, Issue S1 2006C. M. Leonard Although talents and disabilities appear to run in families, direct links between genes and cognitive ability are difficult to establish. Investigators are currently searching for intermediate phenotypes with plausible links to both genome and cognome (the cognitive phenotype). Cortical anatomy could provide one such intermediate phenotype. Variation in cortical size, asymmetry and sulcal pattern is influenced by genetic variation in neurotrophic factors and can predict variation in verbal and mathematical talent. Anecdotal evidence suggests that individuals with a rare morphological variant of Sylvian fissure sometimes have superior visualization ability combined with verbal deficits. Documentation of such ,cognitive cortical syndromes' might prove as genetically informative as the identification of dysmorphic syndromes associated with mental retardation. A necessary prerequisite for the establishment of such syndromes is a reliable technique for the identification of cortical patterns. Recent technical advances in software for automatically labeling and measuring cortical sulci now provide the possibility of establishing standard measures for their shape, size and location. Such measures are a prerequisite for genetic studies of cortical patterns that could illuminate the neurodevelopmental pathways by which genes affect cognitive ability. [source] Enhanced Solid-State Luminescence and Low-Threshold Lasing from Starburst Macromolecular Materials,ADVANCED MATERIALS, Issue 3 2009Wen-Yong Lai High solid-state quantum efficiency (,PL,,,0.90) materials with attractive properties for OLED and laser applications are reported. Our results show that long fluorene chain-lengths are not a necessary prerequisite for efficient solid-state luminescence. Isolated-molecule-like solid-state emission, stable pure-deep-blue electroluminescence, and low-threshold lasing (,laser,=,437,nm, Ethlaser,,,0.4,nJ/pulse, 1.3,µJ cm,2) are demonstrated. [source] GEOMETRICAL, THERMAL AND MECHANICAL PROPERTIES OF OLIVE FRUITSJOURNAL OF FOOD PROCESS ENGINEERING, Issue 2 2010MOHAMAD I. AL-WIDYAN ABSTRACT In Mediterranean countries, olive trees play a significant economical role. Knowledge of olive fruits properties is essential for the efficient handling of the product and optimizing oil yield. The lack of such knowledge at the local level triggered this study in an attempt to report the fruit's chemical composition and some major engineering properties. Established procedures were followed in conducting the measurements and calculations on fruit samples. The study examined four major varieties of olive fruits, including Spanish, Black Spanish, improved Nabali and Nabali Baladi for their chemical composition and other properties, including geometrical, thermal and frictional properties. Thermal properties, including thermal conductivity, heat capacity and thermal diffusivity, ranged from 0.41 to 0.47 W/(m·K), 2.35 to 2.39 kJ/(kg·K) and 2.88 × 10,7to 2.779 × 10,7 m2/s, respectively. The geometrical properties of the Spanish and Black Spanish were quite similar except for roundness and sphericity. Similar results were found for improved Nabali and Nabali Baladi. The properties of weight, density and packing coefficient ranged from 2.22 to 8.60 g, 890 to 1,230 kg/m3 and 0.43 to 0.52, respectively. The fruit's static friction coefficient over mild steel, aluminum and softwood surfaces ranged from 0.20 to 0.30, 0.21 to 0.29 and 0.22 to 0.33, respectively. PRACTICAL APPLICATIONS In Jordan and other Mediterranean countries, olive fruits are produced in large quantities every season. They are very widely used as pickled fruits or are processed in mills to extract their oil. Despite the fact that fruit properties are a necessary prerequisite for the efficient handling and processing of fruits, literature search indicated the lack of a comprehensive study of scientific merit that reports on the engineering properties of olive fruits. In addition, it is established that knowledge of the fruit properties leads to optimized handling and processing and results in knowledge-based development of all processes and equipment that deal with the fruits. The practical merit of this study stems from the fact that it reports on the key properties of a major product (olive fruits) that has social, cultural and economical significance throughout a whole region and is expanding throughout the globe. [source] How many species of cichlid fishes are there in African lakes?MOLECULAR ECOLOGY, Issue 3 2001George F. Turner Abstract The endemic cichlid fishes of Lakes Malawi, Tanganyika and Victoria are textbook examples of explosive speciation and adaptive radiation, and their study promises to yield important insights into these processes. Accurate estimates of species richness of lineages in these lakes, and elsewhere, will be a necessary prerequisite for a thorough comparative analysis of the intrinsic and extrinsic factors influencing rates of diversification. This review presents recent findings on the discoveries of new species and species flocks and critically appraises the relevant evidence on species richness from recent studies of polymorphism and assortative mating, generally using behavioural and molecular methods. Within the haplochromines, the most species-rich lineage, there are few reported cases of postzygotic isolation, and these are generally among allopatric taxa that are likely to have diverged a relatively long time in the past. However, many taxa, including many which occur sympatrically and do not interbreed in nature, produce viable, fertile hybrids. Prezygotic barriers are more important, and persist in laboratory conditions in which environmental factors have been controlled, indicating the primary importance of direct mate preferences. Studies to date indicate that estimates of alpha (within-site) diversity appear to be robust. Although within-species colour polymorphisms are common, these have been taken into account in previous estimates of species richness. However, overall estimates of species richness in Lakes Malawi and Victoria are heavily dependent on the assignation of species status to allopatric populations differing in male colour. Appropriate methods for testing the specific status of allopatric cichlid taxa are reviewed and preliminary results presented. [source] The effect of fungal metabolites on leaves as detected by chlorophyll fluorescenceNEW PHYTOLOGIST, Issue 2 2001Anandini Kshirsagar Summary ,,The effect is reported here of cytochalasin E isolated from the fungus Rosellinia necatrix on photosynthesis in young leaves of Malus domestica (apple). ,,Cytochalasin E was administered via the petiole to excised leaves. The chlorophyll fluorescence emission spectrum and time resolved fluorescence decay were measured up to the point where visible leaf damage was observed. ,,Within 2 h, the ratio of fluorescence emission at 730 nm decreased with respect to the peak at 690 nm. Over 6 h a small blue shift in the 690 nm emission band to 685 nm was seen. The time resolved fluorescence decay showed changes over a similar timescale after administration of cytochalasin E. The control decay could be fitted by two components, ,1, 112 ps, ,2, 402 ps, but after 6 h treatment with cytochalasin E the decay required a further component ,3, 4.25 ns for a good fit. ,,Cytochalasin E has a direct effect on photosynthesis, possibly as a result of impairment of light harvesting. This might partially account for the pathogenicity of the root infecting R. necatrix. Fluorescence techniques may therefore provide an early detection system for the fungus, a necessary prerequisite for development of a control strategy. [source] Uncertain Aims and Tacit Negotiation: Birth Control Practices in Britain, 1925,50POPULATION AND DEVELOPMENT REVIEW, Issue 2 2000Kate Fisher Evidence from oral history interviews is used to suggest the need to reevaluate our understanding of the dynamics of fertility decisions and behavior in the first half of the twentieth century. Those interviewed stressed their vague and haphazard approach to contraceptive use, in sharp contrast to the dominant depiction in studies of fertility decline that emphasize the degree to which individuals made deliberate and calculated choices about family size based on an assessment of the costs and benefits of childrearing. Details of individual contraceptive strategies elucidate the complexities of birth control behavior: couples, lacking explicit aims for family limitation, adopted diverse methods of birth control, using them for different reasons, at different times, with varying degrees of determination and confidence and frequently with very little direct discussion or planning. Explicit articulation of aims was not a necessary prerequisite of the spread of birth control; accepted gender roles meant that responsibilities and obligations emerged gradually and tacitly. As a result, nevertheless, low fertility was effectively achieved. [source] Long-term biomechanical properties of rabbit cornea after photodynamic collagen crosslinkingACTA OPHTHALMOLOGICA, Issue 1 2009Gregor Wollensak Abstract. Purpose:, Photodynamic riboflavin/ultraviolet-A (UVA)-induced collagen cross-linking, which increases the biomechanical stiffness of the human cornea by about 300%, has been introduced recently as a possible treatment for progressive keratoconus. The present study was undertaken to evaluate the longterm biomechanical effects of this new cross-linking treatment as a necessary prerequisite to its clinical success. Methods:, The corneas of the left eyes of nine male rabbits were cross-linked. The contralateral eyes served as controls. After removal of the central 7 mm of the epithelium, the corneas were treated with the photosensitizer riboflavin and UVA irradiation for 30 mins with an irradiance of 3 mW/cm2 using a 370-nm UVA double diode. Groups of three animals were killed immediately after treatment and at 3 and 8 months, respectively. Biomechanical stress,strain measurements were performed using a microcomputer-controlled biomaterial tester on 4 × 10-mm corneal strips. Results:, Corneal thickness in the treated rabbit cornea was 408 ± 20 ,m. A constant and significant increase in ultimate stress (of 69.7,106.0%), Young's modulus of elasticity (of 78.4,87.4%) and a decrease in ultimate strain (of 0.57,78.4%) were found over a time period of up to 8 months after cross-linking treatment. Conclusions:, Riboflavin/UVA-induced collagen cross-linking leads to a longterm increase in biomechanical rigidity which remains stable over time. These data support our previous longterm clinical observations and give hope that this new treatment will halt progressive keratoconus definitively. [source] Beyond competence: defining and promoting excellence in anaesthesiaANAESTHESIA, Issue 2 2010A. F. Smith Summary Recent trends in medical training have tended to focus on competence, in the sense of adequate performance, rather than excellence. This article reviews published literature and relevant concepts relating to excellence and professionalism from within anaesthesia, from medicine more generally and from outside the profession. A number of conceptual frameworks are presented that could be adapted for the promotion of excellence, and some of the necessary prerequisites for this promotion discussed. [source] | ||||||||||||||||